import {
  CubeUVReflectionMapping,
  GammaEncoding,
  LinearEncoding,
  NoToneMapping,
  NearestFilter,
  NoBlending,
  RGBDEncoding,
  RGBEEncoding,
  RGBEFormat,
  RGBM16Encoding,
  RGBM7Encoding,
  UnsignedByteType,
  sRGBEncoding,
, BackSide } from '../constants.js';

import { BufferAttribute } from '../core/BufferAttribute.js';
import { BufferGeometry } from '../core/BufferGeometry.js';
import { Mesh } from '../objects/Mesh.js';
import { OrthographicCamera } from '../cameras/OrthographicCamera.js';
import { PerspectiveCamera } from '../cameras/PerspectiveCamera.js';
import { RawShaderMaterial } from '../materials/RawShaderMaterial.js';
import { Vector2 } from '../math/Vector2.js';
import { Vector3 } from '../math/Vector3.js';
import { Color } from '../math/Color.js';
import { WebGLRenderTarget } from '../renderers/WebGLRenderTarget.js';
import { MeshBasicMaterial } from '../materials/MeshBasicMaterial.js';
import { BoxBufferGeometry } from '../geometries/BoxGeometry.js';


const LOD_MIN = 4;
const LOD_MAX = 8;
const SIZE_MAX = Math.pow(2, LOD_MAX);

// The standard deviations (radians) associated with the extra mips. These are
// chosen to approximate a Trowbridge-Reitz distribution function times the
// geometric shadowing function. These sigma values squared must match the
// variance #defines in cube_uv_reflection_fragment.glsl.js.
const EXTRA_LOD_SIGMA = [0.125, 0.215, 0.35, 0.446, 0.526, 0.582];

const TOTAL_LODS = LOD_MAX - LOD_MIN + 1 + EXTRA_LOD_SIGMA.length;

// The maximum length of the blur for loop. Smaller sigmas will use fewer
// samples and exit early, but not recompile the shader.
const MAX_SAMPLES = 20;

const ENCODINGS = {
  [LinearEncoding]: 0,
  [sRGBEncoding]: 1,
  [RGBEEncoding]: 2,
  [RGBM7Encoding]: 3,
  [RGBM16Encoding]: 4,
  [RGBDEncoding]: 5,
  [GammaEncoding]: 6,
};

const backgroundMaterial = new MeshBasicMaterial({
  side: BackSide,
  depthWrite: false,
  depthTest: false,
});
const backgroundBox = new Mesh(new BoxBufferGeometry(), backgroundMaterial);

const _flatCamera = /* @__PURE__ */ new OrthographicCamera();
const { _lodPlanes, _sizeLods, _sigmas } = /* @__PURE__ */ _createPlanes();
const _clearColor = /* @__PURE__ */ new Color();
let _oldTarget = null;

// Golden Ratio
const PHI = (1 + Math.sqrt(5)) / 2;
const INV_PHI = 1 / PHI;

// Vertices of a dodecahedron (except the opposites, which represent the
// same axis), used as axis directions evenly spread on a sphere.
const _axisDirections = [
  /*@__PURE__*/ new Vector3(1, 1, 1),
  /*@__PURE__*/ new Vector3(-1, 1, 1),
  /*@__PURE__*/ new Vector3(1, 1, -1),
  /*@__PURE__*/ new Vector3(-1, 1, -1),
  /*@__PURE__*/ new Vector3(0, PHI, INV_PHI),
  /*@__PURE__*/ new Vector3(0, PHI, -INV_PHI),
  /*@__PURE__*/ new Vector3(INV_PHI, 0, PHI),
  /*@__PURE__*/ new Vector3(-INV_PHI, 0, PHI),
  /*@__PURE__*/ new Vector3(PHI, INV_PHI, 0),
  /*@__PURE__*/ new Vector3(-PHI, INV_PHI, 0),
];

/**
 * This class generates a Prefiltered, Mipmapped Radiance Environment Map
 * (PMREM) from a cubeMap environment texture. This allows different levels of
 * blur to be quickly accessed based on material roughness. It is packed into a
 * special CubeUV format that allows us to perform custom interpolation so that
 * we can support nonlinear formats such as RGBE. Unlike a traditional mipmap
 * chain, it only goes down to the LOD_MIN level (above), and then creates extra
 * even more filtered 'mips' at the same LOD_MIN resolution, associated with
 * higher roughness levels. In this way we maintain resolution to smoothly
 * interpolate diffuse lighting while limiting sampling computation.
 *
 * Paper: Fast, Accurate Image-Based Lighting
 * https://drive.google.com/file/d/15y8r_UpKlU9SvV4ILb0C3qCPecS8pvLz/view
 */

function convertLinearToRGBE(color) {
  const maxComponent = Math.max(color.r, color.g, color.b);
  const fExp = Math.min(Math.max(Math.ceil(Math.log2(maxComponent)), -128.0), 127.0);
  color.multiplyScalar(Math.pow(2.0, -fExp));

  const alpha = (fExp + 128.0) / 255.0;
  return alpha;
}

class PMREMGenerator {
  constructor(renderer) {
    this._renderer = renderer;
    this._pingPongRenderTarget = null;

    this._blurMaterial = _getBlurShader(MAX_SAMPLES);
    this._equirectShader = null;
    this._cubemapShader = null;

    this._compileMaterial(this._blurMaterial);
  }

  /**
   * Generates a PMREM from a supplied Scene, which can be faster than using an
   * image if networking bandwidth is low. Optional sigma specifies a blur radius
   * in radians to be applied to the scene before PMREM generation. Optional near
   * and far planes ensure the scene is rendered in its entirety (the cubeCamera
   * is placed at the origin).
   */
  fromScene(scene, sigma = 0, near = 0.1, far = 100) {
    _oldTarget = this._renderer.getRenderTarget();
    const cubeUVRenderTarget = this._allocateTargets();

    this._sceneToCubeUV(scene, near, far, cubeUVRenderTarget);
    if (sigma > 0) {
      this._blur(cubeUVRenderTarget, 0, 0, sigma);
    }

    this._applyPMREM(cubeUVRenderTarget);
    this._cleanup(cubeUVRenderTarget);

    return cubeUVRenderTarget;
  }

  /**
   * Generates a PMREM from an equirectangular texture, which can be either LDR
   * (RGBFormat) or HDR (RGBEFormat). The ideal input image size is 1k (1024 x 512),
   * as this matches best with the 256 x 256 cubemap output.
   */
  fromEquirectangular(equirectangular) {
    return this._fromTexture(equirectangular);
  }

  /**
   * Generates a PMREM from an cubemap texture, which can be either LDR
   * (RGBFormat) or HDR (RGBEFormat). The ideal input cube size is 256 x 256,
   * as this matches best with the 256 x 256 cubemap output.
   */
  fromCubemap(cubemap) {
    return this._fromTexture(cubemap);
  }

  /**
   * Pre-compiles the cubemap shader. You can get faster start-up by invoking this method during
   * your texture's network fetch for increased concurrency.
   */
  compileCubemapShader() {
    if (this._cubemapShader === null) {
      this._cubemapShader = _getCubemapShader();
      this._compileMaterial(this._cubemapShader);
    }
  }

  /**
   * Pre-compiles the equirectangular shader. You can get faster start-up by invoking this method during
   * your texture's network fetch for increased concurrency.
   */
  compileEquirectangularShader() {
    if (this._equirectShader === null) {
      this._equirectShader = _getEquirectShader();
      this._compileMaterial(this._equirectShader);
    }
  }

  /**
   * Disposes of the PMREMGenerator's internal memory. Note that PMREMGenerator is a static class,
   * so you should not need more than one PMREMGenerator object. If you do, calling dispose() on
   * one of them will cause any others to also become unusable.
   */
  dispose() {
    this._blurMaterial.dispose();

    if (this._cubemapShader !== null) this._cubemapShader.dispose();
    if (this._equirectShader !== null) this._equirectShader.dispose();

    for (let i = 0; i < _lodPlanes.length; i++) {
      _lodPlanes[i].dispose();
    }
  }

  // private interface

  _cleanup(outputTarget) {
    this._pingPongRenderTarget.dispose();
    this._renderer.setRenderTarget(_oldTarget);
    outputTarget.scissorTest = false;
    _setViewport(outputTarget, 0, 0, outputTarget.width, outputTarget.height);
  }

  _fromTexture(texture) {
    _oldTarget = this._renderer.getRenderTarget();
    const cubeUVRenderTarget = this._allocateTargets(texture);
    this._textureToCubeUV(texture, cubeUVRenderTarget);
    this._applyPMREM(cubeUVRenderTarget);
    this._cleanup(cubeUVRenderTarget);

    return cubeUVRenderTarget;
  }

  _allocateTargets(texture) {
    // warning: null texture is valid

    const params = {
      magFilter: NearestFilter,
      minFilter: NearestFilter,
      generateMipmaps: false,
      type: UnsignedByteType,
      format: RGBEFormat,
      encoding: _isLDR(texture) ? texture.encoding : RGBEEncoding,
      depthBuffer: false,
    };

    const cubeUVRenderTarget = _createRenderTarget(params);
    cubeUVRenderTarget.depthBuffer = !texture;
    this._pingPongRenderTarget = _createRenderTarget(params);
    return cubeUVRenderTarget;
  }

  _compileMaterial(material) {
    const tmpMesh = new Mesh(_lodPlanes[0], material);
    this._renderer.compile(tmpMesh, _flatCamera);
  }

  _sceneToCubeUV(scene, near, far, cubeUVRenderTarget) {
    const fov = 90;
    const aspect = 1;
    const cubeCamera = new PerspectiveCamera(fov, aspect, near, far);
    const upSign = [1, -1, 1, 1, 1, 1];
    const forwardSign = [1, 1, 1, -1, -1, -1];
    const renderer = this._renderer;

    const originalAutoClear = renderer.autoClear;
    const outputEncoding = renderer.outputEncoding;
    const toneMapping = renderer.toneMapping;
    renderer.getClearColor(_clearColor);

    renderer.toneMapping = NoToneMapping;
    renderer.outputEncoding = LinearEncoding;
    renderer.autoClear = false;

    let useSolidColor = false;
    const background = scene.background;
    if (background) {
      if (background.isColor) {
        backgroundMaterial.color.copy(background).convertSRGBToLinear();
        scene.background = null;

        const alpha = convertLinearToRGBE(backgroundMaterial.color);
        backgroundMaterial.opacity = alpha;
        useSolidColor = true;
      }
    } else {
      backgroundMaterial.color.copy(_clearColor).convertSRGBToLinear();

      const alpha = convertLinearToRGBE(backgroundMaterial.color);
      backgroundMaterial.opacity = alpha;
      useSolidColor = true;
    }

    for (let i = 0; i < 6; i++) {
      const col = i % 3;
      if (col == 0) {
        cubeCamera.up.set(0, upSign[i], 0);
        cubeCamera.lookAt(forwardSign[i], 0, 0);
      } else if (col == 1) {
        cubeCamera.up.set(0, 0, upSign[i]);
        cubeCamera.lookAt(0, forwardSign[i], 0);
      } else {
        cubeCamera.up.set(0, upSign[i], 0);
        cubeCamera.lookAt(0, 0, forwardSign[i]);
      }

      _setViewport(cubeUVRenderTarget, col * SIZE_MAX, i > 2 ? SIZE_MAX : 0, SIZE_MAX, SIZE_MAX);
      renderer.setRenderTarget(cubeUVRenderTarget);

      if (useSolidColor) {
        renderer.render(backgroundBox, cubeCamera);
      }

      renderer.render(scene, cubeCamera);
    }

    renderer.toneMapping = toneMapping;
    renderer.outputEncoding = outputEncoding;
    renderer.autoClear = originalAutoClear;
  }

  _textureToCubeUV(texture, cubeUVRenderTarget) {
    const renderer = this._renderer;

    if (texture.isCubeTexture) {
      if (this._cubemapShader == null) {
        this._cubemapShader = _getCubemapShader();
      }
    } else if ( this._equirectShader == null ) {

				this._equirectShader = _getEquirectShader();

			}

    const material = texture.isCubeTexture ? this._cubemapShader : this._equirectShader;
    const mesh = new Mesh(_lodPlanes[0], material);

    const uniforms = material.uniforms;

    uniforms['envMap'].value = texture;

    if (!texture.isCubeTexture) {
      uniforms['texelSize'].value.set(1.0 / texture.image.width, 1.0 / texture.image.height);
    }

    uniforms['inputEncoding'].value = ENCODINGS[texture.encoding];
    uniforms['outputEncoding'].value = ENCODINGS[cubeUVRenderTarget.texture.encoding];

    _setViewport(cubeUVRenderTarget, 0, 0, 3 * SIZE_MAX, 2 * SIZE_MAX);

    renderer.setRenderTarget(cubeUVRenderTarget);
    renderer.render(mesh, _flatCamera);
  }

  _applyPMREM(cubeUVRenderTarget) {
    const renderer = this._renderer;
    const autoClear = renderer.autoClear;
    renderer.autoClear = false;

    for (let i = 1; i < TOTAL_LODS; i++) {
      const sigma = Math.sqrt(_sigmas[i] * _sigmas[i] - _sigmas[i - 1] * _sigmas[i - 1]);

      const poleAxis = _axisDirections[(i - 1) % _axisDirections.length];

      this._blur(cubeUVRenderTarget, i - 1, i, sigma, poleAxis);
    }

    renderer.autoClear = autoClear;
  }

  /**
   * This is a two-pass Gaussian blur for a cubemap. Normally this is done
   * vertically and horizontally, but this breaks down on a cube. Here we apply
   * the blur latitudinally (around the poles), and then longitudinally (towards
   * the poles) to approximate the orthogonally-separable blur. It is least
   * accurate at the poles, but still does a decent job.
   */
  _blur(cubeUVRenderTarget, lodIn, lodOut, sigma, poleAxis) {
    const pingPongRenderTarget = this._pingPongRenderTarget;

    this._halfBlur(cubeUVRenderTarget, pingPongRenderTarget, lodIn, lodOut, sigma, 'latitudinal', poleAxis);

    this._halfBlur(pingPongRenderTarget, cubeUVRenderTarget, lodOut, lodOut, sigma, 'longitudinal', poleAxis);
  }

  _halfBlur(targetIn, targetOut, lodIn, lodOut, sigmaRadians, direction, poleAxis) {
    const renderer = this._renderer;
    const blurMaterial = this._blurMaterial;

    if (direction !== 'latitudinal' && direction !== 'longitudinal') {
      console.error('blur direction must be either latitudinal or longitudinal!');
    }

    // Number of standard deviations at which to cut off the discrete approximation.
    const STANDARD_DEVIATIONS = 3;

    const blurMesh = new Mesh(_lodPlanes[lodOut], blurMaterial);
    const blurUniforms = blurMaterial.uniforms;

    const pixels = _sizeLods[lodIn] - 1;
    const radiansPerPixel = isFinite(sigmaRadians) ? Math.PI / (2 * pixels) : (2 * Math.PI) / (2 * MAX_SAMPLES - 1);
    const sigmaPixels = sigmaRadians / radiansPerPixel;
    const samples = isFinite(sigmaRadians) ? 1 + Math.floor(STANDARD_DEVIATIONS * sigmaPixels) : MAX_SAMPLES;

    if (samples > MAX_SAMPLES) {
      console.warn(
        `sigmaRadians, ${sigmaRadians}, is too large and will clip, as it requested ${samples} samples when the maximum is set to ${MAX_SAMPLES}`,
      );
    }

    const weights = [];
    let sum = 0;

    for (let i = 0; i < MAX_SAMPLES; ++i) {
      const x = i / sigmaPixels;
      const weight = Math.exp((-x * x) / 2);
      weights.push(weight);

      if (i == 0) {
        sum += weight;
      } else if (i < samples) {
        sum += 2 * weight;
      }
    }

    for (let i = 0; i < weights.length; i++) {
      weights[i] = weights[i] / sum;
    }

    blurUniforms['envMap'].value = targetIn.texture;
    blurUniforms['samples'].value = samples;
    blurUniforms['weights'].value = weights;
    blurUniforms['latitudinal'].value = direction === 'latitudinal';

    if (poleAxis) {
      blurUniforms['poleAxis'].value = poleAxis;
    }

    blurUniforms['dTheta'].value = radiansPerPixel;
    blurUniforms['mipInt'].value = LOD_MAX - lodIn;
    blurUniforms['inputEncoding'].value = ENCODINGS[targetIn.texture.encoding];
    blurUniforms['outputEncoding'].value = ENCODINGS[targetIn.texture.encoding];

    const outputSize = _sizeLods[lodOut];
    const x = 3 * Math.max(0, SIZE_MAX - 2 * outputSize);
    const y =
      (lodOut === 0 ? 0 : 2 * SIZE_MAX) +
      2 * outputSize * (lodOut > LOD_MAX - LOD_MIN ? lodOut - LOD_MAX + LOD_MIN : 0);

    _setViewport(targetOut, x, y, 3 * outputSize, 2 * outputSize);
    renderer.setRenderTarget(targetOut);
    renderer.render(blurMesh, _flatCamera);
  }
}

function _isLDR(texture) {
  if (texture === undefined || texture.type !== UnsignedByteType) return false;

  return texture.encoding === LinearEncoding || texture.encoding === sRGBEncoding || texture.encoding === GammaEncoding;
}

function _createPlanes() {
  const _lodPlanes = [];
  const _sizeLods = [];
  const _sigmas = [];

  let lod = LOD_MAX;

  for (let i = 0; i < TOTAL_LODS; i++) {
    const sizeLod = Math.pow(2, lod);
    _sizeLods.push(sizeLod);
    let sigma = 1.0 / sizeLod;

    if (i > LOD_MAX - LOD_MIN) {
      sigma = EXTRA_LOD_SIGMA[i - LOD_MAX + LOD_MIN - 1];
    } else if (i == 0) {
      sigma = 0;
    }

    _sigmas.push(sigma);

    const texelSize = 1.0 / (sizeLod - 1);
    const min = -texelSize / 2;
    const max = 1 + texelSize / 2;
    const uv1 = [min, min, max, min, max, max, min, min, max, max, min, max];

    const cubeFaces = 6;
    const vertices = 6;
    const positionSize = 3;
    const uvSize = 2;
    const faceIndexSize = 1;

    const position = new Float32Array(positionSize * vertices * cubeFaces);
    const uv = new Float32Array(uvSize * vertices * cubeFaces);
    const faceIndex = new Float32Array(faceIndexSize * vertices * cubeFaces);

    for (let face = 0; face < cubeFaces; face++) {
      const x = ((face % 3) * 2) / 3 - 1;
      const y = face > 2 ? 0 : -1;
      const coordinates = [x, y, 0, x + 2 / 3, y, 0, x + 2 / 3, y + 1, 0, x, y, 0, x + 2 / 3, y + 1, 0, x, y + 1, 0];
      position.set(coordinates, positionSize * vertices * face);
      uv.set(uv1, uvSize * vertices * face);
      const fill = [face, face, face, face, face, face];
      faceIndex.set(fill, faceIndexSize * vertices * face);
    }

    const planes = new BufferGeometry();
    planes.setAttribute('position', new BufferAttribute(position, positionSize));
    planes.setAttribute('uv', new BufferAttribute(uv, uvSize));
    planes.setAttribute('faceIndex', new BufferAttribute(faceIndex, faceIndexSize));
    _lodPlanes.push(planes);

    if (lod > LOD_MIN) {
      lod--;
    }
  }

  return { _lodPlanes, _sizeLods, _sigmas };
}

function _createRenderTarget(params) {
  const cubeUVRenderTarget = new WebGLRenderTarget(3 * SIZE_MAX, 3 * SIZE_MAX, params);
  cubeUVRenderTarget.texture.mapping = CubeUVReflectionMapping;
  cubeUVRenderTarget.texture.name = 'PMREM.cubeUv';
  cubeUVRenderTarget.scissorTest = true;
  return cubeUVRenderTarget;
}

function _setViewport(target, x, y, width, height) {
  target.viewport.set(x, y, width, height);
  target.scissor.set(x, y, width, height);
}

function _getBlurShader(maxSamples) {
  const weights = new Float32Array(maxSamples);
  const poleAxis = new Vector3(0, 1, 0);
  const shaderMaterial = new RawShaderMaterial({
    name: 'SphericalGaussianBlur',

    defines: { n: maxSamples },

    uniforms: {
      envMap: { value: null },
      samples: { value: 1 },
      weights: { value: weights },
      latitudinal: { value: false },
      dTheta: { value: 0 },
      mipInt: { value: 0 },
      poleAxis: { value: poleAxis },
      inputEncoding: { value: ENCODINGS[LinearEncoding] },
      outputEncoding: { value: ENCODINGS[LinearEncoding] },
    },

    vertexShader: _getCommonVertexShader(),

    fragmentShader: /* glsl */ `

			precision mediump float;
			precision mediump int;

			varying vec3 vOutputDirection;

			uniform sampler2D envMap;
			uniform int samples;
			uniform float weights[ n ];
			uniform bool latitudinal;
			uniform float dTheta;
			uniform float mipInt;
			uniform vec3 poleAxis;

			${_getEncodings()}

			#define ENVMAP_TYPE_CUBE_UV
			#include <cube_uv_reflection_fragment>

			vec3 getSample( float theta, vec3 axis ) {

				float cosTheta = cos( theta );
				// Rodrigues' axis-angle rotation
				vec3 sampleDirection = vOutputDirection * cosTheta
					+ cross( axis, vOutputDirection ) * sin( theta )
					+ axis * dot( axis, vOutputDirection ) * ( 1.0 - cosTheta );

				return bilinearCubeUV( envMap, sampleDirection, mipInt );

			}

			void main() {

				vec3 axis = latitudinal ? poleAxis : cross( poleAxis, vOutputDirection );

				if ( all( equal( axis, vec3( 0.0 ) ) ) ) {

					axis = vec3( vOutputDirection.z, 0.0, - vOutputDirection.x );

				}

				axis = normalize( axis );

				gl_FragColor = vec4( 0.0, 0.0, 0.0, 1.0 );
				gl_FragColor.rgb += weights[ 0 ] * getSample( 0.0, axis );

				for ( int i = 1; i < n; i++ ) {

					if ( i >= samples ) {

						break;

					}

					float theta = dTheta * float( i );
					gl_FragColor.rgb += weights[ i ] * getSample( -1.0 * theta, axis );
					gl_FragColor.rgb += weights[ i ] * getSample( theta, axis );

				}

				gl_FragColor = linearToOutputTexel( gl_FragColor );

			}
		`,

    blending: NoBlending,
    depthTest: false,
    depthWrite: false,
  });

  return shaderMaterial;
}

function _getEquirectShader() {
  const texelSize = new Vector2(1, 1);
  const shaderMaterial = new RawShaderMaterial({
    name: 'EquirectangularToCubeUV',

    uniforms: {
      envMap: { value: null },
      texelSize: { value: texelSize },
      inputEncoding: { value: ENCODINGS[LinearEncoding] },
      outputEncoding: { value: ENCODINGS[LinearEncoding] },
    },

    vertexShader: _getCommonVertexShader(),

    fragmentShader: /* glsl */ `

			precision mediump float;
			precision mediump int;

			varying vec3 vOutputDirection;

			uniform sampler2D envMap;
			uniform vec2 texelSize;

			${_getEncodings()}

			#include <common>

			void main() {

				gl_FragColor = vec4( 0.0, 0.0, 0.0, 1.0 );

				vec3 outputDirection = normalize( vOutputDirection );
				vec2 uv = equirectUv( outputDirection );

				vec2 f = fract( uv / texelSize - 0.5 );
				uv -= f * texelSize;
				vec3 tl = envMapTexelToLinear( texture2D ( envMap, uv ) ).rgb;
				uv.x += texelSize.x;
				vec3 tr = envMapTexelToLinear( texture2D ( envMap, uv ) ).rgb;
				uv.y += texelSize.y;
				vec3 br = envMapTexelToLinear( texture2D ( envMap, uv ) ).rgb;
				uv.x -= texelSize.x;
				vec3 bl = envMapTexelToLinear( texture2D ( envMap, uv ) ).rgb;

				vec3 tm = mix( tl, tr, f.x );
				vec3 bm = mix( bl, br, f.x );
				gl_FragColor.rgb = mix( tm, bm, f.y );

				gl_FragColor = linearToOutputTexel( gl_FragColor );

			}
		`,

    blending: NoBlending,
    depthTest: false,
    depthWrite: false,
  });

  return shaderMaterial;
}

function _getCubemapShader() {
  const shaderMaterial = new RawShaderMaterial({
    name: 'CubemapToCubeUV',

    uniforms: {
      envMap: { value: null },
      inputEncoding: { value: ENCODINGS[LinearEncoding] },
      outputEncoding: { value: ENCODINGS[LinearEncoding] },
    },

    vertexShader: _getCommonVertexShader(),

    fragmentShader: /* glsl */ `

			precision mediump float;
			precision mediump int;

			varying vec3 vOutputDirection;

			uniform samplerCube envMap;

			${_getEncodings()}

			void main() {

				gl_FragColor = vec4( 0.0, 0.0, 0.0, 1.0 );
				gl_FragColor.rgb = envMapTexelToLinear( textureCube( envMap, vec3( - vOutputDirection.x, vOutputDirection.yz ) ) ).rgb;
				gl_FragColor = linearToOutputTexel( gl_FragColor );

			}
		`,

    blending: NoBlending,
    depthTest: false,
    depthWrite: false,
  });

  return shaderMaterial;
}

function _getCommonVertexShader() {
  return /* glsl */ `

		precision mediump float;
		precision mediump int;

		attribute vec3 position;
		attribute vec2 uv;
		attribute float faceIndex;

		varying vec3 vOutputDirection;

		// RH coordinate system; PMREM face-indexing convention
		vec3 getDirection( vec2 uv, float face ) {

			uv = 2.0 * uv - 1.0;

			vec3 direction = vec3( uv, 1.0 );

			if ( face == 0.0 ) {

				direction = direction.zyx; // ( 1, v, u ) pos x

			} else if ( face == 1.0 ) {

				direction = direction.xzy;
				direction.xz *= -1.0; // ( -u, 1, -v ) pos y

			} else if ( face == 2.0 ) {

				direction.x *= -1.0; // ( -u, v, 1 ) pos z

			} else if ( face == 3.0 ) {

				direction = direction.zyx;
				direction.xz *= -1.0; // ( -1, v, -u ) neg x

			} else if ( face == 4.0 ) {

				direction = direction.xzy;
				direction.xy *= -1.0; // ( -u, -1, v ) neg y

			} else if ( face == 5.0 ) {

				direction.z *= -1.0; // ( u, v, -1 ) neg z

			}

			return direction;

		}

		void main() {

			vOutputDirection = getDirection( uv, faceIndex );
			gl_Position = vec4( position, 1.0 );

		}
	`;
}

function _getEncodings() {
  return /* glsl */ `

		uniform int inputEncoding;
		uniform int outputEncoding;

		#include <encodings_pars_fragment>

		vec4 inputTexelToLinear( vec4 value ) {

			if ( inputEncoding == 0 ) {

				return value;

			} else if ( inputEncoding == 1 ) {

				return sRGBToLinear( value );

			} else if ( inputEncoding == 2 ) {

				return RGBEToLinear( value );

			} else if ( inputEncoding == 3 ) {

				return RGBMToLinear( value, 7.0 );

			} else if ( inputEncoding == 4 ) {

				return RGBMToLinear( value, 16.0 );

			} else if ( inputEncoding == 5 ) {

				return RGBDToLinear( value, 256.0 );

			} else {

				return GammaToLinear( value, 2.2 );

			}

		}

		vec4 linearToOutputTexel( vec4 value ) {

			if ( outputEncoding == 0 ) {

				return value;

			} else if ( outputEncoding == 1 ) {

				return LinearTosRGB( value );

			} else if ( outputEncoding == 2 ) {

				return LinearToRGBE( value );

			} else if ( outputEncoding == 3 ) {

				return LinearToRGBM( value, 7.0 );

			} else if ( outputEncoding == 4 ) {

				return LinearToRGBM( value, 16.0 );

			} else if ( outputEncoding == 5 ) {

				return LinearToRGBD( value, 256.0 );

			} else {

				return LinearToGamma( value, 2.2 );

			}

		}

		vec4 envMapTexelToLinear( vec4 color ) {

			return inputTexelToLinear( color );

		}
	`;
}

export { PMREMGenerator };
